Technical Field
This invention relates to a method and an apparatus for producing a three-dimensional object layer by layer using a powdery material which can be solidified by irradiating it with an energy beam. In particular, the invention relates to the layer-wise application of powder.
Related Art
Equipment for producing a three-dimensional object layer by layer using a powdery material which can be solidified by irradiating it with electromagnetic radiation or an electron beam are known from e.g. U.S. Pat. Nos. 4,863,538, 5,647,931 and SE524467. Such equipment include for instance a supply of powder, means for applying a layer of powder on a working area, and means for directing the beam over the working area. The powder sinters or melts and solidifies as the beam moves over the working area. For product quality reasons it is important that the powder is evenly distributed over the working area and that the layer thickness is well-defined and corresponds to a pre-determined value. Further, it is advantageous that the layer is quickly applied in order to keep the production rate as high as possible.
Traditional powder application means generally includes a feeding member and a distribution member where the former transfers a certain quantity of powder from the supply of powder to the distribution member, which in turn distributes the powder over the working area.
The conditions under which the powder application means work are rough; the temperature is high, powder particles find their way into openings and slits, evaporated powder material condensate and form coatings and the like.
JP 2003245981 discloses a powder application system where a supply of powder is stored onto a feeding member in the form of a height-adjustable plate at the side of a working area. Powder is fed to a distributing rake by a) moving the rake sideways away from the working area and over the supply of powder, b) raising the powder supply plate so that a portion of powder becomes positioned above a lower side of the rake, and c) moving the rake towards and across the powder supply so as to transfer the portion of powder towards the working area. A similar system is disclosed in US 2004/0084814. A drawback of such systems is that it is relatively space consuming.
WO 2006/121374 discloses another powder application system wherein the powder supply is arranged in an open manner such as to form an angle of repose on the side of the powder supply facing the working area. A distribution rake is arranged to be moveable towards and a certain distance into the powder supply such as to bring about a transfer of a portion of powder that flows over the rake from the far side of the distribution rake to the side facing the working area. In a second step, the distribution rake is moved towards and across the working area as to distribute the portion of powder onto the working area. An advantage of this system is that no mechanically operated feeding member is required for feeding powder to the distribution rake.
Problems may arise with the device disclosed in WO 2006/121374 when using certain types of powder that do not flow very well. For instance, powder may stay on top of the rake when the rake is moved into the powder supply and the amount of powder in the portion transferred over the rake may vary.
In WO 2010/095987 it is disclosed yet another powder application system wherein a base surface for supporting supply of powder from a powder storage unit is resilient. A drawback with this design is that the rake has to move into the powder supply which creates unnecessary force on the powder distributor. Another problem is that powder may stick on the back side of the powder distributor which may fall off on a newly distributed powder layer and thereby deteriorate its surface finish.
Thus, there is still a need for improvements in this field.